SSc is associated with significant morbidity and mortality and available therapeutic options have only limited efficacy. Macrophages are thought to play a major role in the pathogenesis of SSc dermal disease because they can alter their phenotype between pro-inflammation and pro-fibrosis/injury resolution. Additionally, recent advances in high-throughput molecular technologies that analyzed whole tissue skin biopsies from SSc patients suggest that macrophages are important cellular targets in SSc, but the precise role macrophages play in SSc dermal fibrosis is unknown. We will take advantage of cutting edge technology that will allow for isolation of macrophages from skin biopsies using multi-parameter flow cytometry and analyze their gene expression profile using RNAseq. Skin biopsies will be obtained from healthy control subjects and from patients with SSc to identify the SSc-specific dermal macrophage signature. We will also obtain skin biopsies from SSc patients before and post mycophenolate mofetil (MMF) treatment and compare signatures between treatment responders and non-responders compared to untreated patients. These studies are timely because recent data from the first randomized double-blinded clinical study suggest that MMF is a useful agent for SSc skin disease. We hypothesize that macrophages are a potential treatment target for patients with SSc dermal disease, and that the new knowledge gained from the proposed studies will shed light upon the role that macrophages play in dermal fibrosis in SSc. These studies, while high-risk, will generate high reward information that has the potential be to paradigm shifting and is ideal for the R21 grant mechanism. !